In conventional or “wet” lithographic printing, ink receptive regions, known as image areas, are generated on a hydrophilic surface. When the surface is moistened with water and ink is applied, the hydrophilic regions retain the water and repel the ink, and the ink receptive regions accept the ink and repel the water. The ink is transferred to the surface of a material upon which the image is to be reproduced. For example, the ink can be first transferred to an intermediate blanket that in turn is used to transfer the ink to the surface of the material upon which the image is to be reproduced.
Imageable elements useful to prepare lithographic printing plates typically comprise at least one imageable layer applied over the hydrophilic surface of a substrate. The imageable layer(s) include one or more radiation-sensitive components that can be dispersed in a suitable binder. Alternatively, the radiation-sensitive component can also be the binder material. Following imaging, either the imaged regions or the non-imaged regions of the imageable layer are removed by a suitable developer, revealing the underlying hydrophilic surface of the substrate. If the imaged (exposed) regions are removed, the element is considered as positive-working. Conversely, if the non-imaged (non-exposed) regions are removed, the element is considered as negative-working. In each instance, the regions of the imageable layer (that is, the image areas) that remain are ink-receptive, and the regions of the hydrophilic surface revealed by the developing process accept water or a fountain solution and repel ink.
Direct digital imaging has become increasingly important in the printing industry. Imageable elements for the preparation of lithographic printing plates have been developed for use with infrared lasers.
Development of negative-working elements using gums is described for example, in EP Publications 1,751,625 (Van Damme et al. published as WO 2005/111727) 1,788,429 (Loccufier et al. et al.), 1,788,430 (Williamson et al.), 1,788,431 (Van Damme et al.), 1,788,434 (Van Damme et al.), 1,788,441 (Van Damme), 1,788,442 (Van Damme), 1,788,443 (Van Damme), 1,788,444 (Van Damme), and 1,788,450 (Van Damme), and WO 2007/057442 (Gries et al.). High pH processing solutions for developing and finishing are described in U.S. Pat. No. 5,035,982 (Walls) and U.S. Pat. No. 6,649,319 (Fiebag et al.). In addition, copending and commonly assigned U.S. Ser. No. 11/872,772 that was filed Oct. 16, 2007 by K. Ray, Tao, Miller, Clark, and Roth) describes negative-working imageable elements that are sensitive to infrared radiation and can be processed using gum solutions.
Copending and commonly assigned U.S. Ser. No. 11/949,817 (filed Dec. 4, 2007 by K. Ray, Tao, and Clark) describes the use of gums to develop imaged UV-sensitive, negative-working imageable elements that contain specific nonpolymeric diamide additives.
U.S. Patent Application Publication 2008/70152 (J. Yu et al.) describes processing of imaged negative-working imageable elements containing copolymers derived from N-methoxymethylmethacrylamide using a highly alkaline developer.
U.S. Patent Application Publication 2007/269739 (Nguyen et al.) describes on-press development of similar elements.